I. Field of Invention
The present invention relates to the field of satellite communication systems, and more particularly, to satellite communication systems employing multi-beam satellites and having built-in redundancy.
II. Related Art
With advances in processor and related technologies, personal computing, whether it be for use in business or for pleasure, is now widely available to large segments of the population. Following the advances of networking and related technologies, many computing devices are now connected to private and/or public networks, such as the Internet or company Intranets, and have access to a wide variety of contents served by a broad range of content servers, such as the World Wide Web (WWW). However, many home or non-business computing users remain frustrated, as they do not have broadband access to support the increasingly rich multi-media contents.
Wire line or fiber optical based broadband access, such as using Digital Subscriber Line (DSL) or Cable Modem systems, are currently very popular. However, wire line based solutions are expensive, and take a long time to achieve pervasive nation or continent wide deployment, if that is even possible, as they require physical cable lines to be installed throughout an entire service or deployment area. As a result, except for the major metropolitan areas or the most newly developed communities, users located in many smaller metropolitan areas or older communities remain without adequate high-speed access to any public or commercial data networks.
Wireless broadband access, if it can be provided efficiently, reliably and inexpensively, is not as restricted. That is, without installing expensive cable over long distances or in less than receptive terrain, every locale across a wide area, including entire countries may be more easily or cost effectively covered.
Concurrently, advances in satellite and related technologies have led to wide spread adoption of Mobile Satellite Services (MSS) for communication. MSS has rapidly moved from servicing simple paging functions to providing voice, and now, data applications, such as accessing a user's email or accessing the Internet or a company Intranet. Accordingly, a need exists to provide inexpensive and reliable satellite based data communication services to a large service area, such as the continental U.S. (referred to as CONUS). It has been believed that a satellite in geosynchronous orbit could service an area the size of the continental United States and provide desired data and services. Generally, Low Earth Orbit (LEO) satellites are viewed as suited for voice traffic, where there is a need for little signal transit delay.
A number of challenges need to be overcome to provide such inexpensive and reliable satellite based data communication service to such a large service area. First of all, while it is possible for a single multi-beam satellite in a geostationary orbit to cover a service area the size of a large country, such as CONUS, a relatively large number of beams, in the range of several tens to a few hundred, would be required to achieve a desired communication link capacity. These beams form tightly-packed “cell” patterns to cover the service area to service a large number of users. However, such an approach has the disadvantage of being costly, as back-up satellites are also required by commercial communication systems to provide an appropriate level of redundancy and reliability, which users have come to depend upon when compared to terrestrial systems. Back up satellites also have to be equally capable of supporting the large number of beams required to cover the entire large service area.
Moreover, it will severely strain the design of satellites employing antenna systems of the popular reflector type, as a large number of feed horns will have to be employed and tightly packed together for each of these reflector antennas. The tightly packed configuration will in turn affect the size of the apertures that can be provided for these feed horns, which in turn negatively impacts beam characteristics such as gain and the beam quality.
Furthermore, the cellular pattern formed may be viewed in a manner similar to that of a terrestrial cellular pattern. In other words, a frequency re-use scheme has to be devised to enable a finite number of assigned or allocated frequencies to be used and shared by the large number of users located within the coverage areas of different, and adjacent, “cells”.
There are also issues with considering and addressing inter-beam interference problems. Such interference needs to be kept to an absolute minimum, regardless of the back up satellite techniques used, as well as with the primary beam forming communications satellites.
Satellite communication systems, and associated terminals or wireless devices manufactured or operating using the teachings of the present invention advantageously addresses these and other challenges to provide less expensive, and more reliable satellite based data communication services, over that of the prior art.